In one aspect, the present invention relates to structures, including alignment films and alignment substrates useful in liquid crystal displays. In another aspect, the invention relates to display devices or other optical devices that utilize liquid crystal alignment films or substrates therein.
A common liquid crystal display, or xe2x80x9cLCD,xe2x80x9d contains an array of two-dimensional picture elements, or pixels. Although each pixel may, and customarily does, contain numerous optical elements, each comprises a liquid crystal cell. A liquid crystal cell generally comprises a liquid crystal material maintained between a pair of transparent substrates. The transparent substrates are most commonly made of glass or a polymeric material. Interposed between the liquid crystal material and the substrates are electrodes electrically connected to an outside signal device that, when electrically active, alter the state of the liquid crystal material. Such liquid crystal cells find application not only is displays, but also in other optical devices, including optical communication devices and other optical processing equipment.
In a liquid crystal cell, the molecules of the liquid crystal material are aligned, or oriented, in a preferred direction along each of the substrates within the cell. Normally, this alignment is accomplished through the use of an alignment structure layer. Alignment structures generally are glass substrates or polymeric films (e.g. polyimides) that are mechanically rubbed in a single direction to impart an orientating effect on the liquid crystals with which they are in contact. Since the rubbing is generally conducted in a single direction, this leads to a pattern of low to high elevations, or topography, across the surface of the alignment structure. The resulting low to high topography creates a measurable angle between the surface of the alignment substrate and the liquid crystal material that is in contact with the alignment structure. This angle is commonly referred to as the xe2x80x9cpre-tiltxe2x80x9d angle. The optical activity of the liquid crystal cell is in part a function of the relative orientation of the liquid crystals at the surface of each substrate and the ordered change in direction of the liquid crystals located between the substrates when the cell is electrically active. When the alignment layer has an appreciable pre-tilt angle, the liquid crystals between the substrates will order predominately in a single, controlled direction of orientation when the cell is in an electrically active state. This uniform orientation improves the optical clarity of the cell by reducing the amount of undesirable scattering that would otherwise result if multiple orientations were possible. Additionally, the alignment structures can be chemically resistant to common solvents.
Although alignment structures derived from conventional rubbing techniques can provide pre-tilt control and chemical resistance, these structures suffer many drawbacks associated with the mechanical rubbing. For example, the high temperatures necessary to process many useful polymeric substrates prevent the incorporation of temperature-sensitive adhesives and color dyes into the alignment structure. Variations in the mechanical rubbing process and generation of debris also inhibit uniformity in the alignment structure over large surface areas. Additionally, the conventional rubbing, washing, and drying steps used in manufacture of the alignment structures can be slow, expensive, and introduce gross defects and low yields. There exists, therefore, a need for an alignment structure that can cure the problems associated with mechanical rubbing while maintaining pre-tilt control and/or chemical resistance.
Briefly, in one aspect, the present invention provides an alignment structure comprising a substrate having disposed thereon an oriented layer of a chromonic liquid crystalline material, wherein the chromonic liquid crystalline material comprises a chromonic material and a pre-tilt additive. This aspect of the invention can also provide an alignment structure comprising a substrate having disposed thereon an oriented layer of a chromonic material, wherein the alignment structure has a pre-tilt angle of between about 5 and 90 degrees. The structures of this aspect of the invention can be made by coating a solution of a chromonic liquid crystalline material onto a substrate and drying the coated substrate. Liquid crystal cells can also be constructed by disposing a liquid crystal material between two parallel display panel substrates and disposing the alignment structure on at least one of the substrates. A plurality of these liquid crystal cells can be used to make a liquid crystal display. Liquid crystal displays can also be made wherein the liquid crystal cells are arranged in a multi-domain pattern.
In another aspect the invention provides an alignment structure comprising a substrate having disposed thereon an oriented layer of a chromonic liquid crystalline material, wherein the chromonic liquid crystalline material comprises a chromonic material and a cross-linking agent. This aspect of the invention can also provide an alignment structure comprising a substrate having disposed thereon an oriented layer of a cross-linked chromonic material. The structures of this aspect of the invention can be made by coating a solution of a chromonic liquid crystalline material onto a substrate and curing the coated substrate. Liquid crystal cells can also be constructed by disposing a liquid crystal material between two parallel display panel substrates and disposing the alignment structure on at least one of the substrates. A plurality of these liquid crystal cells can be used to make a liquid crystal display. Liquid crystal displays can also be made wherein the liquid crystal cells are arranged in a multi-domain pattern.
In yet another aspect the invention provides an alignment structure comprising a substrate having disposed thereon an oriented layer of a chromonic liquid crystalline material, wherein the chromonic liquid crystalline material comprises a chromonic material, a pre-tilt additive, and a cross-linking agent. This aspect of the invention can also provide an alignment structure comprising a substrate having disposed thereon an oriented layer of a cross-linked chromonic material, wherein the alignment structure has a pre-tilt angle of between about 5 and 90 degrees. The structures of this aspect of the invention can be made by coating a solution of a chromonic liquid crystalline material onto a substrate and then curing the coated substrate. Liquid crystal cells can also be constructed by disposing a liquid crystal material between two parallel display panel substrates and disposing the alignment structure on at least one of the substrates. A plurality of these liquid crystal cells can be used to make a liquid crystal display. Liquid crystal displays can also be made wherein the liquid crystal cells are arranged in a multi-domain pattern.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The detailed description and figures which follow more particularly exemplify these embodiments.